A variety of rationales have been developed over the years to subdivide our classification
files into searchable units. Collections of art based on each of the following rationales
can be found in the system as it exists today. Thus, keep in mind the strengths and
weaknesses of each rationale when conducting a search.
1. Industry or Use
This approach divides art on the basis of the industry employing the art or the use
to which a device is put. It provides a unique collection wherein all relevant devices
for a given technology are housed in one convenient location. Several original classes
were created using this rationale and a number of these classes still exist today,
e.g., Bee Culture, Butchering, etc.
A drawback of classifying in the above manner is that physically similar art is separated
without a meaningful distinction. Thus, the search process is lengthened. If the
above classification process is used excessively, there is a greater chance of issuing
two patents for the same idea. To illustrate, the 1872 classification system separated
cooling devices on the basis of the product treated in these devices; e.g., beer
or milk. These cooling devices could well be analogous and both should be considered
in performing any search for cooling devices, per se.
2. Proximate Function
To avoid fragmenting the art based on its industry or use, the U.S. Patent and Trademark
Office uses the fundamental, direct, or necessary function as the principal basis
of classification. Also, for brevity, the term “proximate” is substituted for the
words fundamental, direct, or necessary. Therefore, “proximate” function means that
similar processes or structures that achieve similar results by the application of
similar natural laws to similar substances are considered to have the same fundamental
utility and are grouped together. Our current system provides a single collecting
area for all heat exchange devices; e.g., milk coolers, beer coolers, etc. Once collected
into this single area, the art is further subdivided on features essential to heat
The term “utility” refers to (1) the function that a process, structure, or composition
can perform; (2) the effect of a process, structure, or composition; or (3) the product
that is produced by a process, structure, or composition. The proximate function,
when used as a basis for classification, is generally applied to a process, structure,
or composition for performing general operations in which a single causative characteristic
can be identified and which requires essentially a single unitary act; e.g., agitating,
cutting, heating, filtering, etc.
This rationale collects art into industrial or trade groupings based on the result
produced by the art. This result may be tangible (e.g., the product of a manufacturing
process) or intangible (e.g., the communication of sound at a distance). In the mechanical
and electrical fields, this method of grouping is generally reserved for complex
processes or structures requiring successive manipulations involving plural acts;
e.g., telephone system, shoemaking machine, etc. In the chemical fields, processes
involving chemical reactions often are classified on the basis of the product produced.
Simple subject matter having no apparent functional characteristics is classified
based on the structural configuration or physical makeup of the object. This situation
rarely arises with respect to the creation of a large group or class in mechanical
fields, but frequently occurs with respect to subdivisions within such group or class.
A chemical compound is always classified on the basis of structure, and a stock material
is often classified on the basis of structure. The chemical structure of compounds
and the components and arrangement of the components of a stock material determine
their classification, irrespective of the utility or utilities involved.
Since the properties of mixtures, or compositions, are not predictable to the same
degree as are the properties of chemical compounds, utility is usually the primary
basis for classification of mixtures. In the case of certain mixtures, however, such
as colloids and alloys, the best classification seems to be on the basis of the components
The following description is a brief overview of the USPC system. This description
will acquaint you with terms and phrases used in the handbook. Many of these terms
and phrases are explained in greater detail later in this handbook.
A fundamental principle of the USPC system is that each class, or part thereof, was
1. analyzing the claimed disclosures of the U.S. patents ,
2. creating various divisions and subdivisions on the basis of that analysis rather
than by making a theoretical arrangement or ordering, and, finally ,
3. classifying the patent documents into the arrangement .
In the USPC system, similar subject matter has been gathered in large groupings to
create classes. Each class was then subdivided into smaller searchable units called
subclasses. The sequence or pattern arrangement of the subclasses within each class
is indicated by the Class Schedule.
Each class and its subclasses, with the exception of alpha subclasses of the utility
classes and some of the design classes, have a title and a definition. The title
and definition of any subclass in a class schedule are further restricted (a) by
the title and definition of the class and (b) by the title and definition of any
subclass or subclasses under which they are indented.
The bulk of patent documents stored in the USPC system are U.S. patents. These documents
are designated as either “OR” (Original) or “XR” (Cross-Reference) placements. The
USPTO began publishing U.S. patent applications in March of 2001, and they too are
stored in the USPC. These documents, referred to as PGPub documents as they are “Pre-Grant-Publications”,
have a mandatory classification called a “Primary” classification and may additionally
include “Secondary” classifications.
The OR classification is based on the claims in the patent. It is a mandatory classification
assigned to a patent that has the same class as the class of the controlling claim.
Only patents designated as Originals in a subclass are used, in conjunction with
the definition of the subclass, to define the “body of art” encompassed by the subclass
for the purpose of determining where newly filed applications are best assigned for
A Cross-Reference placement is an additional classification added to a patent to
a different subclass in the system. Refer to Section V and Section VI in this handbook
for more information on this subject.
Every PGPub document must have one, and only one “Primary” classification. The Primary
classification for a PGPub document is representative of the main inventive concept
within the complete disclosure, using the claims as a guide.
PGPub documents may also be assigned “Secondary” classifications based on invention
information, or other information considered to be valuable for search. Assignment
of secondary classifications based on invention information is mandatory, while Secondary
classifications based on non-inventive, but otherwise valuable, information are discretionary.
The USPC system also contains many foreign patent documents and non-patent literature
references. The procedure for classifying foreign patent documents and non-patent
literature in the system is simpler than the procedure for classifying U.S. patent
documents. Total disclosure is generally used in classifying foreign patent documents
and non-patent literature.
Until October 1, 1995, the U.S. Patent and Trademark Office received copies of foreign
patent documents from other countries and classified them into the USPC system. Beginning
in October 1995, however, newly published foreign patent documents were no longer
classified into the USPC system. USPTO now receives most foreign patents on CD-ROM
disks. These foreign patents on CD-ROM are accessible from the Foreign Patents Branch
of the Scientific and Technical Information Center, through the Foreign Patents Access
Also, after October 1, 1995, copies of foreign documents in the examiner files were
no longer automatically reclassified during a USPC reclassification project. In some
cases, the foreign documents associated with a reclassification project remain in
the old US classifications, which are transformed into “Foreign Patent Art Collections.”
These collections appear at the end of the class that includes the newly created
U.S. subclasses. Foreign Patent Art Collections are identified by their subclass
numbers, which include the prefix “FOR,” followed by a 3-digit number.
Each Foreign Patent Art Collection contains, in parentheses at the end of the title,
the subclass number in which the foreign patent documents were classified before
the reclassification project.
Subclass definitions are maintained for the Foreign Patent Art Collections that exactly
correspond to those of the former classification schedule.
Some foreign patents continue to be filed in the examiner search files by IPC class.
See attachment B to Section IV of the Manual of Classification for a listing.
E-subclasses are USPC subclasses that are equivalent in scope to classifications
in the European Classification system, ECLA, on a one-to-one basis. These subclasses
appear at the end of the USPC class schedules in which they exist (at the time of
this writing, they exist only in class 257) and can be identified by their subclass
numbers, which begin with the letter “E”.
E-subclasses represent a transitional harmonization effort by the USPTO to begin
using ECLA classifications. The definitions of E-subclasses state which ECLA classification
the E-subclass corresponds to. It may or may not provide a detailed description of
the metes and bounds of the art encompassed by the subclass.
The documents classified in E-subclasses should be reviewed to determine the subject
matter encompassed by an E-subclass whenever the scope of the subclass cannot be
determined from the title or its definition.
E-subclasses are similar to cross-reference art collections in that they cannot take
original placements of U.S. patents or Primary classifications of PGPub documents.
At the time of their creation, E-subclasses are populated with documents from their
equivalent ECLA classifications. Subsequently, U.S. patent documents are classified
and maintained in E-subclasses by USPTO, while the classification and maintenance
of non-JP foreign documents is performed by EPO. Foreign documents are regularly
placed in the E-subclasses through the DOCDB data supplied to USPTO by the EPO.
An E-subclass title ending with the expression “(EPO)” indicates that documents classified
by the EPO have been and are regularly placed in the subclass. An E-subclass title
may also include a “(JPO)” suffix which indicates the subclass has JP documents placed
by the JPO. This would typically be done for E-subclasses corresponding to IPC level
classifications. Even though an E-subclass may not have documents placed by JPO,
it should be remembered that EPO has placed many JP documents into ECLA that are
classified in the E-subclasses.
In rare instances, an E-subclass may have no “(EPO)” or “(JPO)” suffix on its title.
This indicates the subclass was created solely by USPTO and that there is no equivalent
ECLA classification. These E-subclasses are not regularly populated with foreign
art from the EPO or JPO. In order to review foreign patent documents pertinent to
the subject matter provided for by these E-subclasses, one must review the documents
classified in the parent subclass that does provide for them.
When an examiner or classifier places a mandatory classification for a U.S. document
in a subclass whose title begins with a parenthesized “(E)”, at least one cross-reference
classification is normally assigned to an E-subclass at the end of the class schedule.
Mandatory classification include OR and Primary classifications, as well as any mandatory
XR and Secondary classifications.
Specific search tools are used to access information contained in the system. The
following discussion provides detailed information on these tools and how to use
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